[Bug c++/64931] New: ICE on function with deduced return type and input is instantiated template class

["sneves at dei dot uc.pt" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64931

            Bug ID: 64931
           Summary: ICE on function with deduced return type and input is
                    instantiated template class
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sneves at dei dot uc.pt

Minimal example:

template<typename T, unsigned long N>
struct array {
  T data[N];
};

auto copy(array<int, 32> const& x) {
  return x;
}

This only seems to result in ICE if a) `copy` has deduced return type with
value semantics, i.e. `auto` but not `decltype(auto)`, and b) if the `array`
struct is a template, and `copy` takes in a specific instantiation of `array`.
Verified to ICE in GCC 4.8.2, 4.9.2, and 5.0.0 20150202.